1. Field of the Invention
The present invention relates to the preparation of p-aminophenols from the corresponding nitrobenzenes, and, more especially, to the preparation of p-aminophenolic compounds and N-acylated derivatives thereof that are optionally substituted on their respective aromatic nucleii.
The present invention more particularly relates to the preparation of p-aminophenol, a valuable compound economically, because it is a useful intermediate for the production of N-acetyl-p-aminophenol ("APAP").
2. Description of the Prior Art
It is known to this art to prepare p-aminophenols from phenylhydroxyl amines via the Bamberger Rearrangement (E. Bamberger, Ber., 27, 1347, 1548 (1894)).
Phenylhydroxyl amines are prepared by a careful reduction of nitrobenzene.
A direct route for the preparation of p-aminophenol entails the catalytic reduction of nitrobenzene. This reaction is carried out in an aqueous medium, in the presence of a strong acid, and in particular sulfuric acid, as well as a hydrogenation catalyst, generally platinum deposited onto a support.
p-Aminophenol production can be accompanied by the formation of byproducts such as aniline, 4-amino-4'-hydroxydiphenyl amine, 4-amino-4'-hydroxydiphenyl ether, 4,4'-dihydroxydiphenyl amine and 4,4'-diaminodiphenyl ether.
In order to limit the formation of byproducts, it is also known to this art to include additives in the process sequence, which are either catalyst poisons such as sulfur compounds (U.S. Pat. No. 4,571,437), or surfactants (U.S. Pat. No. 4,176,138).
The processes described in the aforesaid patents consequently require the use of supplementary additives.